The present invention generally relates to enhanced implantable biomedical devices and instruments, and more particularly to implantable biomedical devices and instruments having sonomicrometer functions incorporated therein.
Using the time-of-flight principle of high frequency sound waves, it is possible to accurately measure distances within an aqueous medium, such as inside the body of a living being. High frequency sound, or ultrasound, is defined as vibrational energy that ranges in frequency from 100 KHz to 10 MHz. The device used to obtain dimensional measurements using sound waves is known as a xe2x80x9csonomicrometerxe2x80x9d. A typical sonomicrometer uses two or more piezoelectric transducers that act as transmitters and receivers of ultrasound energy when situated in a sound-conducting medium and connected to electronic circuitry. The distance between transducers is measured by first electrically energizing the transmitting transducer, causing it to produce ultrasound energy. The resulting sound wave then propagates through the medium until it is detected by the receiving transducer. The propagation time of the ultrasound signal, when multiplied by the velocity of sound in the medium, yields the distance between transducers.
The transducers typically take the form of a piezoelectric ceramic (e.g., PZT or PVDF material) that are energized by a voltage spike, or impulse function of a designated duration. This causes the transducer to oscillate at a characteristic resonant frequency that results in a transmitted signal which propagates away from the transmitter through the medium.
The receiver detects the sound energy produced by the transmitter and begins to vibrate in response thereto. This vibration produces an electronic signal on the order of millivolts that can be amplified by appropriate receiver circuitry.
The propagation velocity of ultrasound in many materials is well documented. The distance traveled by a pulse of ultrasound can therefore be measured simply by recording the time delay between the instant the sound is transmitted and when it is received. This process of transmission and reception can be repeated many times per second. Depending on the embodiment, a large matrix of distances between many transducers can be obtained. In U.S. Pat. Nos. 5,515,853; 5,795,298; and 5,797,849 (fully incorporated herein by reference), a procedure is explained for determining the spatial {x,y,z} coordinates for each transducer from the distance matrix.
Presently, there are several classes of biomedical devices that perform electrical or mechanical activity within the body that do not incorporate dimension-measurement technology as part of their operation. It is believed that the absence of this technology is due to the lack of awareness of sonomicrometry by biomedical engineers, leading to a low appreciation of the utility and benefits of sonomicrometry.
The present invention addresses the foregoing problem, as well as others, to provide implantable biomedical devices which collect dimension-measurement data using sonomicrometer technology.
According to the present invention there is provided an implantable biomedical device which uses sonomicrometry to provide dimension-measurement data that enhances the functionality of the biomedical device.
An advantage of the present invention is the provision of a cardiac pacemaker which is capable of acquiring cardiac dimensional data and calculating from that data parameters such as heart rate, contractile amplitude, contractility, cardiac size, stroke volume and ventricular ejection fraction.
Another advantage of the present invention is the provision of a cardiac defibrillator which is capable of acquiring cardiac dimensional data and calculating from that data parameters such as heart rate, contractile amplitude, contractility, cardiac size, stroke volume and ejection fraction, wherein the cardiac dimensional data and/or computed parameters may be used to determine the need to apply a defibrillation shock, and/or optionally to evaluate post-shock cardiac contractility.
Still another advantage of the present invention is the provision of a ventricular assist device which is capable of acquiring cardiac dimensional data and computed parameters that provide feedback and control information, wherein the information is suitable for determining the appropriate or optimal interaction between the heart and assist device. The nature of this interaction could, for example, pertain to ventricular size, filling or ejection rate, or cardiac output.
Yet another advantage of the present invention is the provision of a post-operative cardiac monitoring device which is capable of acquiring cardiac dimensional data, wall thickness data, and computed parameters such as heart rate, contractile amplitude, contractility, cardiac size, stroke volume and ejection fraction, wherein the cardiac dimensional data and computed parameters can be used to adjust drug doses and treatment protocols during recovery, and to evaluate cardiac function.
These advantages and others are provided by the biomedical apparatus of the present invention in which an implantable biomedical device is provided for providing biomedical assistance to a body structure, and including a device controller for regulating the operating of the biomedical device.
A sonomicrometer arrangement is provided, in contact with the body structure and in communication with the device controller. This sonomicrometer arrangement ultrasonically measures at least one physical parameter of the body structure and provides feedback information to the device controller. The device controller regulates the operation of the biomedical device in response to the feedback information.
Still other advantages of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description, accompanying drawings and appended claims.